A 64-year-old asymptomatic man is found to have a serum IgG kappa M-protein of 3.4 g/dL. Bone marrow biopsy shows 18% clonal plasma cells. Hemoglobin, calcium, creatinine are normal, skeletal survey shows no lytic lesions, and free light chain ratio is 1.4. What is the most likely diagnosis?
- A Monoclonal gammopathy of undetermined significance
- B Smoldering multiple myeloma ✓
- C Solitary plasmacytoma of bone
- D Waldenstrom macroglobulinemia
Correct answer: B. Smoldering multiple myeloma
Explanation
Smoldering myeloma is defined by an M-protein of 3 g/dL or more and/or clonal bone marrow plasma cells between 10% and 60%, in the absence of CRAB features or myeloma-defining biomarkers. MGUS requires both an M-protein below 3 g/dL and plasma cells below 10%, so the 18% clone excludes it. Solitary plasmacytoma is a single osseous or extraosseous lesion, and Waldenstrom requires an IgM paraprotein with lymphoplasmacytic marrow infiltrate.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.